Plainsman

Are there any good examples where shallower rim depths (30mm or less) tested faster than deeper sections (30-55mm)? With all of the current wind tunnel data floating about, and the evolution of aero rims from deep V to semi-toroidal to wide, I’m guessing there must be some modern shallow rims that produce less drag than older deep sections, OR, at a certain point does a sufficiently deep rim outperform its shallow counterpart simply due to the increase in depth?

79pmooney

I"m sure there are examples of deeper rim being poorer than a shallow one. The exact shape matter a whole lot. Wind angle does also. It is very likely that a good shallower rim will out-perform a deeper rim in a cross-headwind.

Orion12521

I can give some annecdotal feedback on rim depth, but it is from my persepective and I'm physically not an "average" cyclist - and philosophically, is anyone? So I am heavier for a cyclist. I'm generally weighing between 170 and 185 lbs and I'm 5'11". When I had "racing" and "training" wheels, I ran a 30mm alloy rim for the "training" wheels and a 50mm carbon rim for "race" wheels. I would also ride the "race" wheels for non-race events, but was more selective regarding conditions. Windy day? Stick with the alloy, because the effect of crosswinds moving me around was greater. Pretty much all of my wheels are built up 24 spoke front and 28 rear. Personally I put more value on durability than being the lightest possible wheelset.

About 6 years ago I made a change regarding wheels and sold off the "training" and "race" wheelsets and went with a 38mm carbon clincher front and rear, still in 24 spoke front and 28 rear counts. I ride them for everything, racing, training, recreational, touring... I believe they hit the sweet spot of providing an aero advantage while maintaining a small enough cross section that I don't feel like I'm getting blown all over the road. Again, I'm heavier than a lot of people. Would I feel a greater effect if I weighed 150 lbs? Probably. Could I "optimize" things by having multiple wheelsets? Probably... but there is an additional cost associated with each additional wheelset. The benefits? I do all my riding on the same wheelset, whether it is racing, training or leisure. There are no surprises regarding traction, braking feel/responsiveness or how they feel spinning up. I also don't have to worry about whether I changed the pad spacing to accommodate the "narrow" alloy rim or the "wide" carbon rim, or for that matter whether I have the alloy pads in or the carbon. When I want to ride I just pump up the tires and go. It is one less variable that I have to think of, and for me provides value through the added simplicity.

Kimmo

AFAIK, the long-held consensus is that you need at least a 3:1 aspect ratio for a shape to have any significant aero. So for a 25mm tyre real benefits only happen at 50mm and above.

Anecdotally, I've had a couple of semi-aero (25-30mm) wheelsets, and they didn't do much. Pre pandemic I dropped AU$1800 on a set of 50mm tubulars, and they're mad AF. The set weighs 1080g, and I can totally feel the aero; the faster you go, the faster they feel. I weigh about 75kg and haven't found crosswinds to be at all troubling with this modern fat profile (couldn't keep using my 7700 brake; had to get a 9000 one). You're more conscious of crosswinds, but it's nothing like the skinny sharp rim craziness.

The braking on these Caden rims is pretty sensational too, which was a surprise.

HTupolev

Deep rims tend to maintain low CdA out to greater yaw angles than shallow. Avoidance of deep rims in crosswinds is generally a matter of steering effects, not resistance to forward motion.

rsbob 

Shallower is faster for hill climbing and from a standing start because they are lighter. Shallow can also be less tricky in stiff cross winds. Deep sections are faster on the flats but slower from a dead stop. It all depends on the kind of riding you do. Can a shallow be faster as an all around wheel than deep section? It depends on how you ride (commuter, competitor, recreational).

This site has some helpful info: https://www.lightbicycle.com/newslet...Do-I-Need.html

Or if you do AI: “Based on the search results provided, it is possible for a shallow profile bike rim to be faster than a deep section bike rim in certain circumstances. According to one of the search results, shallow wheels are typically lighter, which can make the bike feel faster, while deeper rims are generally more aerodynamic. However, crosswinds can catch deeper rims and make them slower, while shallower rims can be more stable in windy ”

DangerousDanR

Hambini has a lot of test results for different brands and sizes of wheels. And it is in writing so you don't need to listen to Hambini!
https://www.hambini.com/bicycle-whee...a-50km-h-disc/

Kimmo

Guess you missed the part where I said my 50mm wheels weigh less than 1.1kg

Russ Roth

Typically no, even with a slight weight advantage there isn't much going for a shallow rim even when climbing. The lighter wheel can feel faster on a climb, but unless there are stops involved, it isn't really faster since the heavier rim can maintain speed better. Excepting start/stops with commuting or extreme cross winds a lighter, shallower rim just isn't better. Even then, how much lighter is the light rim? One of the cherished light rims is the open pro which weighted around 420ish grams from the ones I've weighed before building up, my newest velocity Aileron at 27mm deep was only 440g which is decent for aluminum and the 32mm mavic cxp pro carbon rim was only 410g. My newest 45mm deep rims for my cross bike are less then 450g. Not too heavy compared to some of the older climb dynamic rims that were so light in the 90s.

79pmooney

I find the idea that those rims are light a little amusing. I used to train on rims that weighed 330 gm and raced 290s. 400 was a winter rim. Yes, very shallow and not aero at all. And despite the opinions I read now, much more comfortable over rough roads than any rim today.

rsbob 

Why yes I indeed did because I wasn’t addressing you, but the OP. But I am very happy for your 50s. My Hunt60s weigh 1669 But the set only cost $1200.

Russ Roth

Starting in a shop in the 90s and building wheels, I only ever came across 1 set of rims that were lighter, a local racer brought in a set of older late 80s rims that were light, somewhere in the mid 300g range. They never stayed straight, every third race required a retrue. He had them rebuilt at another shop and the results were worse. The mavic reflex was 395g as I recall but the clincher versions had failure issue and the tubular was beefed up though still stayed around 400g. The only thing I can remember being under 400g were the bmx race rims but they were 420iso rims and narrow to boot. And I spent a lot of time perusing the QBP catalog to build my first race set which was a pair of velocity razor which were much flatter and barely weighted above 400g, the lightest I could find in the qbp catalog in 97.

Bah Humbug

Over in Ironman world, at least a few years ago it was becoming trendy to run 30mm fronts at Kona because it was faster to stay in aero on the descent from Hawi, while the deeper wheels had people up on the bullhorns white-knuckling and unable to make up the difference on the flats. That's not quite the question, of course - depth is not everything but matters enough that it tends to dwarf other effects. How small of a depth difference will the OP accept? 30mm well-shaped rims would likely be faster than 35mm Vs.

terrymorse 

It depends on how fast you are going on those climbs. If you're climbing at speeds under ~10 mph, light weight wins out over aero every time.

The whole "heavy rims act like flywheels so they go faster uphill" idea is a bunch of hooey.

For most of us, there's one big factor that makes going uphill easier, and it's reducing weight.

Personally speaking, if a hill climb TT grade is 6% or less, I'd choose some aero wheels. 7% or above, and I'd look for the lightest wheels I can find.

Kontact 

But then you're losing top speed on the descents, assuming you don't only race uphill.

Certainly the wheelset Kimmo has demonstrates that you can have both, if you're willing to pay. I'm not willing to pay even $1200, so I have 1100 gram alloy wheels and don't worry about being the fastest rider. But light wheels feel better than aero ones.

terrymorse 

Maybe you’ll be a bit slower on the downhill, but you spend a lot less time descending than climbing, and descending speed has more to do with skills than how aero you+bike are.

urbanknight

Ignoring the whole point of this thread for now, if you can make a 1100g wheelset at 50mm, wouldn't logic suggest you could make a 25mm set even lighter if you use the same materials and construction?

Kontact 

Maybe, except carbon fiber likes bigger sections to regain stiffness lost by thinner walls. Carbon bikes with narrow tubes aren't lighter, so why would skinny carbon rims be lighter?

Plus, you're eliminating 1 inch x 44 pieces of spoke by using taller rims, or the equivalent of 4 fewer spokes.

Kimmo

Yours are probably clinchers, and probably disc, right?

The cheaper option (no straight pull) from Caden in 60mm clincher disc weighs 1710g and costs more, so I wouldn't sweat it.

The point was, tubular is how you get light and deep, and the seat of the pants feel is one of phenomenal performance. Carbon tubulars are also a way less sketchy proposition than carbon clinchers too, particularly rim brake. I think the rim weight for my 50s is 330g or so, pretty mad.

Pity about the damn tubes being sewn in, but at least we have sealant these days...

My advice to anyone thinking about getting their first set of deep carbon wheels, is go the whole hog and do tubulars. It's worth the hassle for a fully mental wheelset.

Kimmo

Velocity Aerohead was a 400g rim, and worked pretty good as a 24h front. Brake tracks were too light for rear use though, potholes would bend them. Not sure if it's still a thing, but back in the 90s they were a good fraction as popular as the Deep V.

Russ Roth

The Aerohead was what turned me on to Velocity, currently the family has a total of 15 bikes with velocity rims, but their weight was falsely advertised and fluctuated a bit but often matched with the open pro. I did find them strong enough, even at 230 I never had a problem with the sidewalls unless it was wearing through the brake track as it was definitely a softer aluminum. I currently have a front in the basement with no rear, the rear finally wore through the brake track about 5 years ago but it was old enough I bought it when they were still made in Australia. Their mtb version the aeroheat was another story, I think I had a half dozen dents in the front and rear rims each. I've found their newest version, now called the dyad, to be fine on my gravel bike but interestingly they don't offer the dyad in a mtb version any more, though I guess its now too narrow to be a mtb rim.

rsbob 

I have 60MM wheels sporting tubeless and they make a phenomenal difference on the flats. Comfort and speed, what’s not to like?

aliasfox

I'd actually say that for purposes of control, a shallower wheel is often better on a descent. If I'm hitting 40+mph between switchbacks, I definitely want to feel like I can hit my line when the turn comes, and not feel like I need to fight a gust of wind. Maybe not as much of a concern on a descent with gentle curves (say, descending Kings Mountain into the valley vs La Honda towards the coast, for those familiar with riding around Silicon Valley).

Kimmo

A 50mm rim with a modern wide profile, with a 23 on the front, is actually no problem in strong gusts. It's the Goldilocks depth.

aliasfox

Possibly, though I’ve definitely felt it more on my 45mm carbon wheel than the 30mm it replaced. Not enough to throw me off my line when I felt it (granted, straight and flat rail trail), but noticeable.